The crowd began gathering before 10:00 a.m., many queuing up in the line that would reward the first 100 people with free coffee for a year. There was music from one of Boston’s top pop radio stations and voices guests recognized as popular DJs. Mascots from Boston’s professional sports teams romped through the crowd, posing for pictures and high-fives. This was the scene before they cut the ribbon signifying the reopening of a Dunkin’ shop. It’s a scene that has played out in cities across the country, but none with the history of this one, home to Dunkin’ Store No. 1. As Rick Colón, Dunkin’s chief operating officer, remarked, “It’s amazing that the brand started right here on this corner, 70 years ago. This is an important part of our brand journey.”